The inner-shell photoionization of highly charged ions by polarized beam of incident photons and their subsequent radiative decay are studied within the framework of density-matrix theory and by using the multi-configuration Dirac-Fock approach (MCDF). Final state density matrix has been derived for the system "photoelectron plus ion" with a well defined geometry. This density matrix allows further to evaluate polarization Stokes parameters for the x-ray photons emitted in the radiative decay of the excited ionic states. Detailed polarization calculations have been performed for the 2p53s→2p6 radiative transitions following ionization of the 2p electron of the sodiumlike iron Fe15+ and uranium U81+ ions.